An essential step to any photopolymeric relief printing process is the development of the printing plate after image formation. Ordinarily, this is accomplished by washing the exposed plate in a solvent which can remove the unpolymerized material while leaving the polymerized (cured) material intact. Since such plates can be formed from a variety of materials, it is necessary to match the specific plates with the appropriate solvent.
For example U.S. Pat. Nos. 4,323,636, 4,323,637, 4,423,135, and 4,369,246 disclose a variety of photopolymer printing plate compositions based on block copolymers of styrene and butadiene (SBS) or isoprene (SIS). These compositions can be utilized to produce printing plates which can be developed by an array of aliphatic and aromatic solvents including methyl ethyl ketone, toluene, xylene, carbon tetrachloride, trichlorethane, methyl chloroform, and tetrachloroethylene. These solvents may be used by themselves or in a mixture with a "non-solvent" (i.e. a material which cannot dissolve unpolymerized materials e.g. trichloroethane with ethanol). In either case, during the development step the solvent can be applied in any convenient manner such as by pouring, immersing, spraying, or roller application. Brushing, which aids in the removal of the unpolymerized or uncrosslinked portions of the composition, can also be performed to facilitate the plate processing.
Similarly, British No. 1,358,062 discloses photosensitive compositions consisting of a nitrile rubber with an addition photopolymerizable tri- or tetra-unsaturated ester derived from acrylic or methacrylic acid combined with an addition polymerization initiator activatable by actinic radiation. Plates made from these compositions are processable by organic solvents including aliphatic esters such as ethyl acetate, aliphatic ketones such as acetone, methyl ethyl ketone or halogentated organic solvents such as methylene chloride, Freon.RTM. and blends of such solvents. Brushing or agitation can be used to facilitate the removal of the non-polymerized portion of composition.
U.S. Pat. No. 4,177,074 discloses a photosensitive composition containing a high molecular weight butadiene/acrylonitrile copolymer which contains carboxyl groups, a low molecular weight butadiene polymer which may or may not contain carboxyl groups, and an ethylenically unsaturated monomer, combined with a free-radical generating system. This composition has use as a flexographic printing plate and requires processing organic solvents including methyl ethyl ketone, benzene, toluene, xylene, trichloroethane, trichlorethylene, methyl chloroform, tetrachloroethylene, or solvent/non-solvent mixtures e.g. tetrachloroethylene and n-butanol. The composition may also be processed with water soluble organic solvents in aqueous basic solution, such as sodium hydroxide/isopropyl alcohol/water; sodium carbonate isopropyl alcohol/water; sodium carbonate/2-butoxyethanol water; sodium borate/2-butoxyethanol/water; sodium silicate/2-butoxyethanol/water; sodium borate/2butoxyethanol/water; sodium silicate/2-butoxyethanol / glycerol/water; and sodium carbonate/2-(2-butoxyethoxy) ethanol/water.
U.S. Pat. No. 4,517,279 discloses a photosensitive composition containing a high molecular weight butadiene acrylonitrile copolymer which contains carboxyl groups, and a high molecular weight butadiene/acrylonitrile copolymer which does not contain carboxyl groups, combined with ethylenically unsaturated monomer and a free radical generating system. This composition, which has use as a flexographic printing plate, requires processing by a tetrachloroethylene solvent in blends of tetrachloroethylene and a non solvent. This composition may also be processed in mixtures of sodiu hydroxide/isopropyl alcohol/water, sodium carbonate/2-butoxyethanol/water, sodium silicate/2-butoxyethanol/water, sodium carbonate / 2-butoxyethanol/glycerol/water and sodium hydroxide/2-(2-butoxyethoxy) tthanol/water.
Thus, the solvents needed for image development will vary depending on the composition of the plate employed. This is quite inconvenient, especially if different photopolymer systems are to be processed at the same facility. Furthermore, many of the solvents used to develop the plates are toxic or suspected carcinogenic materials. Thus, there exists real need for solvent systems which can be used with a higher degree of safety. There exists a need for solvent systems which can be used in a variety of plates.